JP2000074635A - Three-dimensional camera and method for recording surface structure of prescribed object by triangulation - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a three-dimensional camera and method which are particularly used for dental surgery for recording the surface structure of a prescribed object by triangulation. SOLUTION: A three-dimensional camera incorporates a light beam generating means 3 which generates a group of light beams for irradiating a prescribed object 8 through projected-light routes 1 and 1', an image sensor which receives the light rays scattered backward by means of the object 8 through an observational-light route 9, and a means which is installed to the routes 1 and 1' and generates a pattern to be projected upon the object 8. The camera contains triangulation angle changing means 4 and 10 in the routes 1 and 1' and/or 9 and triangulation angles are controlled by the angles between the center beams of the routes 1 and 1' and that of the route 9. At least two times of three-dimensional measurement are performed on the same object 8 at different triangulation angles α and α'.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a three-dimensional (3-D) camera for recording the surface structure of a predetermined object by triangulation, and particularly to a three-dimensional dental camera. This 3
The three-dimensional camera includes means for generating a group of light beams, the group of light beams may be guided through a projection light path from a first direction to a predetermined object and illuminate the predetermined object. The three-dimensional camera further includes an observation light path with an image sensor for receiving light scattered backward by a given object. An angle is provided between the projection light path and the observation light path, so that a three-dimensional measurement is possible. Further, means for generating a reference pattern to be projected on the predetermined object are arranged in the projection light path.

[0002] Such a three-dimensional camera (that is, a camera for recording a three-dimensional structure) is disclosed in the magazine "Measurement: Sensors, Devices, and Systems" (Technisches Messen: Sensor).
en, Gerate, Systeme ”, June 1996, pages 254-261, Oldenbo
urg-Verlag B3020). Its technical content is incorporated in its entirety in the present application.

US Pat. No. 4,575,805 discloses a three-dimensional camera capable of recording the surface structure of a predetermined object as a height difference or a depth difference. This known three-dimensional camera makes an angle with the optical axis of the three-dimensional camera,
It has a projection light path and an observation light path. A light source for emitting a group of light beams in the direction of a given object is located in the projection light path. Light reflected by a predetermined object is guided to an image sensor of a three-dimensional camera through an observation light path. The signal from the image sensor can be provided to an evaluation unit, whereby an image of the surface structure can be created on the display. The three-dimensional camera is particularly suitable for recording holes in teeth.

[0004] EP-A-0 250 993 also discloses a three-dimensional camera as follows. Means are provided for generating the reference pattern in such a manner that the reference pattern can be projected onto the surface structure in order to determine the height difference or depth difference of the surface structure. Phase shift triangulation, referred to as phase shifting triangulation and associated with evaluation electronics to perform the method described in more detail in the above-mentioned document, utilizes the light reflected by the surface structure and incident on the image sensor to modify the surface structure. , Height difference and depth difference, and can be represented as a pseudo three-dimensional image on a monitor.

It is clear from the above references that the reference pattern projected onto the surface structure is preferably a linear reference pattern that can be generated by an LCD arrangement or a mechanical grating. For each predetermined period of the reference pattern, there is a clear range, that is, a range in which the height difference between two points of the object can be clearly recorded, which is represented by the following equation.

Clear range = period of reference pattern / tangent of angle between projection light path and observation light path.

[0007] The achievable measurement accuracy is always a fraction (typically one hundredth) of the clear range, as it is limited by electrical noise and other effects. Therefore, if the period is long, the clear range is large, but the height difference between two points of the object cannot be recorded very precisely. If the period is short, the clear range becomes small, but the height difference between two points of the object can be recorded very precisely.

Since it is desirable to be able to record clear and precise large differences in elevation between two points on an object, DE 90 13
454 U1 proposes a three-dimensional camera in which means for generating a first reference pattern and a second reference pattern for a given object are provided in the projection light path.
By projecting a reference pattern having a different period preferentially onto a predetermined object, a substantially larger height difference between two points of the object can be clearly recorded as compared with a case where only one reference pattern is used. .

A disadvantage of this device is that the first grid is
And the overall accuracy achieved is reduced or a longer recording time is required. Overall, the design costs are very high.

[0010] Here, furthermore, even in the case of unfavorable surface structures, it can be guided to a given object through a further projection light path from a second direction different from the first direction, in order to be able to measure the surface structures. Further means for generating a further group of light beams are proposed. This makes it possible to illuminate the surface structure from different directions, and it is proposed to arrange means for generating a reference pattern in each projection light path.

A disadvantage of this device is that the manual operation of the three-dimensional camera itself adds expense to the device, and therefore, devices that are easy to handle are difficult to manufacture.

This disadvantage is described in WO 98/11 403.
It is also present in A1. WO 98/11 403 A1
For the three-dimensional measurement of objects by optical recording, pattern projection and triangulation calculations, the projection unit and the recording unit for the pattern can be constructed separately and positioned or introduced independently of each other during the measurement process. A method and apparatus are disclosed.

[0013]

SUMMARY OF THE INVENTION It is, therefore, an object of the present invention to achieve a clear measurement when there is a large elevation difference without reducing the accuracy of the measurement, but also while keeping the cost of the apparatus low.

The object is to provide means for generating a group of light beams for illuminating a given object through a projection light path, and an image sensor for receiving light scattered backward by the given object through an observation light path. And by means of a three-dimensional camera, in particular for dentistry, for recording the surface structure of a given object by triangulation, comprising means in the projection light path for generating a pattern to be projected on the given object. Achieved.

According to the invention, the three-dimensional camera comprises means for changing the triangulation angle defined by the angle between the central beam of the projection light path and the central beam of the observation light path, by means of the projection light path and / or Or it is included in the observation light path.

The means for changing the triangulation angle changes the center beam of the projection light path and / or the observation light path. By providing these means, it is possible to obtain a clear measurement value while maintaining a simple structure when there is a large height difference.

According to one refinement, the means for changing the triangulation angle is a diaphragm whose shape and / or position can be changed. By opening and closing the aperture, the center beam can be shifted, but for that purpose an asymmetric aperture is required.

According to another refinement, the means for changing the triangulation angle is a shadow plate inserted in the projection light path and / or the observation light path, in particular in the form of a flag driven by a solenoid.

In another configuration, a diaphragm having a liquid crystal whose light transmission can be changed is used.

Furthermore, it is advantageous to change both the path of the central beam in the projection light path and the path of the central beam in the observation light path in order to have a greater effect on the difference in the triangulation angles.

A particularly suitable angle for the triangulation angle is 3
° to 15 °, triangulation angle from 3% to 50%
Can be changed.

Another measure for achieving this object is a method for recording the surface structure of a given object by triangulation, especially for dentistry. In the method according to the invention, three-dimensional measurements of the same predetermined object are taken at least twice successively at closely spaced temporal intervals, and the distance between the center beam of the projection light path and the center beam of the observation light path is determined. The triangulation angle can be slightly changed between the two measurements. This change in triangulation angle changes the record of the measured object, from which the three-dimensional morphology of the object can be calculated.

Advantageously, the triangulation angle is varied by a factor taking a value greater than or equal to 0.7 and less than 1, or by a factor greater than 1 and less than or equal to 1.3. That is, the triangulation angle is reduced to at least 0.7 times its initial value,
Alternatively, it is increased to a maximum of 1.3 times its initial value. In this range, a good increase in the clear range can be achieved, provided that the signal is of good quality. The closer the coefficient of the triangulation angle change is to 1, the better the signal must be.

Advantageously, the change of the triangulation angle after the first measurement shadows or opens the projection light path and / or the observation light path by means of an aperture which can be changed in shape and / or position. This is done by shifting the position of the center beam.

[0025]

DETAILED DESCRIPTION In FIG. 1, a projection light path 1 is defined by a first group of light beams 2 that can be generated by means 3. Means 3 may for example comprise LEDs and lenses. The projection light path 1 is represented by a central beam. The term central beam is intended to mean a beam that is averaged over the intensity and cross-sectional area of the group of light beams 2. More precisely, this means that the position of the central beam at the cross-sectional surface of the group of light beams is obtained by averaging the weights of the point coordinates in the cross-section with the respective light intensities at the points in the cross-section. Means For a group of circular light beams with uniform intensity, the center beam passes through the center of the circle.

A group of light beams 2 of the projection light path 1 enters the prism tube 5 through the stop 4 and after being deflected by the prism 6 at a predetermined angle with respect to the longitudinal axis of the prism tube 5, A group of light beams emerge from the prism tube. The group of light beams emerging from the prism tube 5 through the prism 6 is represented by the center beam, but the surface 7 of the object 8 to be measured
And is scattered backward from there.

The light scattered backward is applied to the observation light path 9.
Pass along. The center beam of the observation light path 9 is the surface 7
And an angle α called the triangulation angle is included between the projection light path and the observation light path. The light scattered backward by the predetermined object 8 is again deflected along the observation light path 9 through the prism 6 and the prism tube 5
Then, the light is sent to the image sensor 11 through the second aperture 10. The image sensor 11 converts the received optical signal into an electrical signal, which is a signal known from the literature cited at the outset to obtain data from which an image of the surface structure of a given object 8 can be created. Sent to the processing unit.

The optical elements required to form the image of the object on the image sensor are not shown for the sake of simplicity, as well as to form the image of the grid on the object and the grid itself. Necessary optical elements are not shown. This structure is also described in the above-mentioned magazine,
Apparatus and System ", page 257, also shown and described in FIG.

Critical in the subject of the invention is the arrangement of the means for offsetting the central beams in the projection light path 1 and the observation light path 9, respectively. In the drawing, the stop 4 is designed in such a way that the central beam 1 is shifted upward, as represented by the dashed line 1 ', so that shadows can be produced in the region below it. Partly shaded aperture 4
Following the projection light path 1 ′ with, it can clearly be seen that the triangulation angle α has been reduced, and this reduced angle is therefore denoted α ′.

When a shadow is cast on the aperture, the center beam shifts,
Therefore, the optical signal received by the image sensor 11 is attenuated as compared with the optical signal measured by opening the aperture. The exact manner in which the center beam is shifted is not directly important in the basic principles of the invention. But the aperture is
For example, it could be shadowed by a slide driven by a solenoid that moves relative to the stop to increase reproducibility. An alternative recalled is a diaphragm whose shape and / or position can be changed, or alternatively, a pin hole diaphragm controlled by an LCD array. In selecting the means used to change the center beam, optimal use of available space is an essential factor.

The following describes how two records at slightly different triangulation angles can be calculated for a clear measurement result that goes beyond the original clear range of the individual record.

In FIG. 2, the height measurements xα, xα ′ obtained from two measurement records according to the invention are plotted against the actual height profile z of the measured object.

In this case, the diagram is of the "sawtooth" type, since the individual measurement records are unclear. The period of this "saw tooth" is the clear range (E) of the individual record.
It can be seen that the larger the value of z, the greater the difference between the measured values xα and xα ′. Thus, from this difference, a conclusion can be drawn as to which distinct range (order) the points of the object are located in. If you know the order,
The absolute height value z can be calculated from xα and xα 'as shown for the medium heights Z1, Z2 and Z3. For this purpose, only the correct multiple of E is added to the value xα. Through such calculations on the values xα and xα ′ from the individual records, the ambiguity of the individual records is removed. The double recording is clear in the multiple range, and more precisely, as can be seen with some thought, the clear range as a result of the double recording is a factor α / (α−
α '). At a typical value on which the idea according to the invention is based, an improvement by a factor of 10 is obtained.

The measurement accuracy (noise) provided by the first measurement with the triangulation value α does not change in this case, since only a fixed value E is repeatedly added to the measurement value. This is true even if the quality of the second recording degrades, for example due to lower light intensity.

The movement of the camera relative to the object between the two measurement records does not similarly affect the measurement accuracy for the same reason, and at worst has the effect of adding the wrong multiple of E.

By the double triangulation method without ambiguity,
An absolute measurement of the position of the measured object with respect to the camera is made possible.

These may be used, for example, for subtle correction of errors in optical image formation or positioning errors by the user.

[Brief description of the drawings]

FIG. 1 is a diagram showing a basic light path of a three-dimensional camera.

FIG. 2 is a diagram showing a measured height profile.

[Explanation of symbols]

1 projection light path, 2 groups of light beams, 3 means, 4
Stop, 5 prism tube, 6 prism, 7 surface, 8 object, 9 observation light path, 10 second stop, 1
1 Image sensor.

 ──────────────────────────────────────────────────の Continued on the front page (72) Inventor Axel Schbözer Germany, 64521 Gross-Gerau, Auf del Carbusbenu, 21

Claims (10)

[Claims] Means for generating a group of light beams for illuminating a predetermined object through a projection light path; and a predetermined object through an observation light path. A dental sensor, especially including an image sensor for receiving light scattered backward by (8), and means in the projection light path (1, 1 ') for generating a pattern to be projected onto a given object. Three-dimensional camera for recording the surface structure of a given object by triangulation, between a center beam of a projection light path (1, 1 ') and a center beam of an observation light path (9). By means of triangulation, characterized by means (4, 10) in the projection light path (1, 1 ') and / or the observation light path (9) for changing the triangulation angle defined by the angle Three-dimensional camera for recording the surface structure of a given object Mela. 2. The means for changing the triangulation angle is a stop (4, 10) whose shape and / or position can be changed and through which the direction of the center beam can be changed. A three-dimensional camera for recording a surface structure of a predetermined object by the triangulation method according to claim 1. 3. The means for varying the triangulation angle comprises a projection light path (1, 1 ') and / or an observation light path (9), in particular in the form of a flag driven by a solenoid.
A three-dimensional camera for recording a surface structure of a predetermined object by a triangulation method according to claim 1 or 2, further comprising a shadow plate inserted into the three-dimensional camera. 4. The three-dimensional camera for recording a surface structure of a predetermined object by a triangulation method according to claim 2, wherein the aperture has a liquid crystal whose light transmission can be changed. . 5. The path of the central beam of the projection light path (1, 1 ') and the path of the central beam of the observation light path (9) can both be changed by suitable means for changing the triangulation angle. A three-dimensional camera for recording a surface structure of a predetermined object by a triangulation method according to any one of claims 1 to 4, wherein the three-dimensional camera can record the surface structure of a predetermined object. 6. The method according to claim 1, wherein said triangulation angle is in the range of 3 ° to 15 °.
A three-dimensional camera for recording a surface structure of a predetermined object by the triangulation method according to any one of the above. 7. The surface structure of a predetermined object by the triangulation method according to claim 1, wherein the angle of the triangulation method can be changed from 3% to 50%. Three-dimensional camera for recording images. 8. A method for recording the surface structure of a given object by triangulation, in particular for dentistry, wherein at least one of the same given object (8) is successively arranged at close intervals in time. Two three-dimensional measurements are made and the projection light path (1,
The triangulation method characterized in that the triangulation angle (α, α ′) between the central beam of 1 ′) and the central beam of the observation light path (9) is slightly changed between the two measurements. A method for recording the surface structure of a given object according to: 9. The method according to claim 8, wherein the triangulation angle is reduced to a minimum of 0.7 times its initial value and increased to a maximum of 1.3 times its initial value. For recording the surface structure of a given object by triangulation. 10. A projection light path and / or a stop (4, 10) of variable shape and / or position.
Or by shading or opening the observation light path, the center beam is displaced and the triangulation angle change is made after the first measurement,
A method for recording the surface structure of a given object by triangulation according to any one of claims 8 and 9.